Squamous Cell Carcinoma In Situ of the Breast: Report of a Case.

We present the case of a 73-year-old woman with pure squamous cell carcinoma in situ of the left breast. This non-invasive malignancy exhibited pure squamous type of architectural and cytologic features without any evidence of glandular differentiation either in the initial needle core biopsy or in the subsequently performed excisional biopsy and simple mastectomy. The tumor spanned 1.6 cm, involved numerous ducts and terminal ducts and extended into lobules, and was characterized by keratinizing squamous cells with intermediate-grade nuclei. Intercellular bridges extended between the malignant squamous cells. Keratinous debris with "pearl" formation was evident in most involved glands. No invasive carcinoma was identified. There was no evidence of metastatic disease in the ipsilateral sentinel lymph nodes. Thus far, only three cases of squamous cell carcinoma in situ of the breast have been reported in one series-none of which showed any evidence of recurrent or metastatic disease at last follow-up. In our case, treated exclusively by surgery, there was no evidence of disease 11 years after diagnosis.